The present invention generally relates to a piezoelectric device and, more particularly, to a piezoelectric resonator utilizing a direction-oriented electroconductive plastic sheet.
The term "direction-oriented electroconductive plastic sheet" is to be understood herein as meaning an electroconductive plastic sheet having such a property as to exhibit an electroconductivity in a predetermined direction across the thickness of the plastic sheet, in contrast to an ordinary electroconductive plastic sheet which exhibits its electroconductivity isotropically. The direction-oriented electroconductive plastic sheet is a recent development and a very few years have passed since it was made available commercially. The direction-oriented electroconductive plastic sheet is generally made of a sheet of silicone rubber containing electroconductive material, for example, metallic particles, carbon particles or metallic fibers, dispersed therein in a predetermined arrangement, and is currently commercially available in two types: one is an anisotropically electroconductive plastic sheet capable of exhibiting its electroconductivity only in a predetermined direction across the thickness of the plastic sheet while the other is a pressure-conductive plastic sheet which is similar in property to that of the anisotropically electroconductive plastic sheet, but requires the application of pressure to establish the electroconductivity across its thickness.
The present invention pertains to a utilization of the direction-oriented electroconductive plastic sheet in a piezoelectric device as a connector element.
There is known a piezoelectric device, for example, a piezoelectric resonator, utilizing a face vibration mode or a radial vibration mode, an example of which is shown in FIG. 1 of the accompanying drawings in side elevational view. Referring to FIG. 1, the conventional piezoelectric resonator comprises a piezoelectric substrate 1 of a plate-like configuration having its opposed surfaces coated or deposited with electrode layers 6 and 7, and a pair of metallic terminal elements 2 and 3 having respective protuberances 4 and 5. This piezoelectric substrate 1 is supported in position between the metallic terminal members 2 and 3 by the protuberances 4 and 5 contacting the electrode layers 6 and 7 at respective positions corresponding to nodes of vibrations of the piezoelectric substrate 1.
In the conventional piezoelectric device, in order for the piezoelectric substrate 1 to be securely supported and to be securely electrically connected to the metallic terminal elements 2 and 3, the metallic terminal elements 2 and 3 are resilient enough to urge the protuberances 4 and 5 against the piezoelectric substrate 1 through the associated electrode layers 6 and 7 and to hold the piezoelectric substrate 1 in position. However, in view of the particular supporting system and the limited types of material that can be used in it, the conventional piezoelectric resonator has no room for improvement as to protection against vibrations and/or impacts.
In order to render the piezoelectric resonator resistant to vibration and impact, it has heretofore been suggested to use additionally an elastic polymer compound, such as a synthetic rubber, or a spring element, or to utilize terminal elements of electroconductive polymer compound in place of the metallic terminal elements.
Japanese Laid-open Patent Publication No. 52-110547 and Japanese Laid-open Utility Model Publications No. 52-122630, No. 52-122631 and No. 52-122632, all of which were laid open to public inspection in 1977, each disclose a piezoelectric resonator of a type having three terminal elements and utilizable as a filter. In this prior art piezoelectric resonator having first, second and third terminal elements, one of the opposed surfaces of the piezoelectric substrate is coated or deposited with a common electrode layer over its entire surface and is electrically connected to the first terminal element through an elastic protuberance protruding outwards from the first terminal element and contacting the common electrode layer. The other surface of the same piezoelectric substrate is provided with a central electrode layer and a second electrode layer electrically insulated from and encircling the central electrode layer, both of which are electrically connected respectively to the second and third terminal elements through corresponding elastic protuberances which protrude outwards from the second and third terminal elements and contact the central and surrounding electrode layers, respectively.
Even in this prior art piezoelectric resonator of the type having the three terminal elements, all of the terminal elements are made of a resilient metallic material, since there has been no method for supporting the piezoelectric substrate other than relying on the resiliency of the terminal elements.
On the other hand, some manufacturers of piezoelectric resonators are exposed to severe competition and must, therefore, minimize manufacturing costs while improving the performance of their products. In view of this, it has long been desired to provide high quality piezoelectric resonators that are simple in construction and the manufacture of which can be automated.